Efficient communication of network identifiers

ABSTRACT

There is provided a method of operating a terminal device in a first network, the method comprising maintaining one or more indices and a mapping between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein two or more networks and/or network nodes share the same index; and in the event that the terminal device is to take an action in respect of a network and/or network node having an index shared with another network and/or network node, the method further comprises the step of determining which one of the two or more networks and/or network nodes having the shared index the terminal device is to take the action in respect of. Methods of operating a node and network nodes are also provided.

This application is the National Stage of International Application No. PCT/SE2015/051218, which claims the benefit of U.S. Provisional Application No. 62/085,958, filed Dec. 1, 2014, the disclosures of which are fully incorporated herein by reference.

TECHNICAL FIELD

The techniques described herein relate to the communication of network identifiers, for example identifiers of wireless local area networks, WLANs, between a terminal device and a network node, or between network nodes.

BACKGROUND

The wireless local-area network (WLAN) technology known as “Wi-Fi” has been standardized by IEEE in the 802.11 series of specifications (i.e., as “IEEE Standard for Information technology—Telecommunications and information exchange between systems. Local and metropolitan area networks—Specific requirements. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”).

Cellular operators that are currently serving mobile users with, for example, any of the technologies standardized by the 3rd-Generation Partnership Project (3GPP), including the radio-access technologies known as Long-Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS)/Wideband Code-Division Multiple Access (WCDMA), High Speed Packet Access (HSPA) and Global System for Mobile Communications (GSM), see Wi-Fi as a wireless technology that can provide good additional support for users in their regular cellular networks. There is interest around using the Wi-Fi technology as an extension, or alternative to cellular radio access network technologies to handle the always increasing wireless bandwidth demands. The term “operator-controlled Wi-Fi” points to a Wi-Fi deployment that on some level is integrated with a cellular network operator's existing network and where the 3GPP radio access networks and the Wi-Fi wireless access may even be connected to the same core network and provide the same services.

3GPP is currently working on specifying a feature/mechanism for WLAN/3GPP Radio interworking which improves operator control with respect to how a UE performs access selection and traffic steering between 3GPP and WLANs belonging to the operator or its partners. Three different solutions have been described in 3GPP TR 37.834 v12.0.0 (2013-December) “Study on Wireless Local Area Network (WLAN)—3GPP radio interworking (Release 12)”.

In one of the solutions (Solution 2 in TR 37.834), which is also referred to as the “threshold-based mechanism” herein, the 3GPP network (i.e. network node of the first RAT) provides to the UE (the term used to refer to a terminal device by 3GPP) conditions and/or thresholds which are used by the UE in one or more pre-defined rules dictating when the terminal device should steer traffic from one RAT to the other.

In another one of the solutions (Solution 3 in TR 37.834), which is also referred to a “traffic steering command based mechanism” herein, the (3GPP) network configures the UE to send measurement reports related to WLANs the terminal device has discovered (or to WLANs for which certain conditions have been fulfilled). The network would, based on these measurement reports, decide whether the terminal device shall steer traffic towards the reported WLANs. If a terminal device is to steer traffic towards a WLAN, the network sends a traffic steering command to that terminal device.

In both of the above solutions, identifiers of WLANs (also referred to as WLAN identifiers) may need to be communicated between the radio access network, RAN, and the UE. In the threshold-based mechanism, the RAN may communicate a list of WLAN identifiers to the UE that are acceptable for the UE to consider when evaluating the pre-defined rules. In the traffic steering command based mechanism, the RAN may communicate a list of WLAN identifiers to the UE that the UE is to measure, and the UE may communicate the identity of one or more WLANs (i.e. the WLAN identifiers) that fulfill the conditions to the RAN.

WLAN identifiers are large, for example, a Service Set Indicator (SSID) may be up to 32 bytes. The communication of the WLAN identifiers between the RAN and UE (and between nodes in the network in the event that the WLAN identifier list is provided from one node to another) can therefore generate a lot of signaling between the network and the UE just to identify WLANs. This signaling will decrease system capacity, increase terminal device power consumption, generate interference, etc.

A similar problem exists for other types of WLAN identifiers, such basic SSIDs, BSSIDs, extended SSIDs, ESSIDs, homogenous ESSIDs, HESSIDs, Realm identifiers, Network Access Indicators, NAIs, public land mobile network, PLMN, identifiers, or Domain Name lists, as well as identifiers for networks operating according to other radio access technologies (RATs).

It will be appreciated that these problems are not confined to the communication of network identifiers as part of an interworking mechanism, and that they can arise in other situations where one or more network identifiers are communicated between a UE and network node (or between network nodes).

Therefore, there is a need for a technique for the efficient communication of network identifiers, for example identifiers of WLANs, between a terminal device and a network node, or between network nodes.

SUMMARY

According to a first aspect, there is provided a method of operating a terminal device in a first network, the method comprising maintaining one or more indices and a mapping between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein two or more networks and/or network nodes share the same index; and in the event that the terminal device is to take an action in respect of a network and/or network node having an index shared with another network and/or network node, the method further comprises the step of determining which one of the two or more networks and/or network nodes having the shared index the terminal device is to take the action in respect of.

According to a second aspect, there is provided a terminal device for use in a first network, the terminal device being adapted to maintain one or more indices and a mapping between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein two or more networks and/or network nodes share the same index; and determine which one of the two or more networks and/or network nodes having the shared index the terminal device is to take an action in respect of in the event that the terminal device is to take an action in respect of a network and/or network node having an index shared with another network and/or network node.

According to a third aspect, there is provided a method of operating a node in a first network, the method comprising maintaining one or more indices and a mapping between the one or more indices and respective network identifiers in an array or a table, each network identifier identifying a network and/or a network node; and in communications between the node and another node in the first network in which a particular network and/or a particular network node is to be identified, using the index associated with the particular network and/or the particular network node to identify the particular network and/or the particular network node.

According to a fourth aspect, there is provided a node for use in a first network, the node being adapted to maintain one or more indices and a mapping between the one or more indices and respective network identifiers in an array or a table, each network identifier identifying a network and/or a network node; and use the index associated with the particular network and/or the particular network node to identify the particular network and/or the particular network node in communications between the node and another node in the first network in which a particular network and/or a particular network node is to be identified.

According to a fifth aspect, there is provided a method of operating a network node in a first network, the method comprising determining one or more indices and a mapping between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein different mappings are determined for different terminal devices and/or network subscribers; and sending the one or more indices and the mapping to another network node in the first network or to a terminal device in the first network.

According to a sixth aspect, there is provided a network node for use in a first network, the network node being adapted to determine one or more indices and a mapping between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein different mappings are determined for different terminal devices and/or network subscribers; and send the one or more indices and the mapping to another network node in the first network or to a terminal device in the first network.

According to a seventh aspect, there is provided a method of operating a network node in a first network, the method comprising maintaining one or more indices and one or more mappings between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein different mappings apply to different terminal devices and/or network subscribers; and in communications between the network node and a terminal device in which a particular network and/or a particular network node is to be identified, using the index associated with the particular network and/or the particular network node in the mapping that applies to the terminal device to identify the particular network and/or the particular network node.

According to an eighth aspect, there is provided a network node for use in a first network, the network node being adapted to maintain one or more indices and one or more mappings between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein different mappings apply to different terminal devices and/or network subscribers; and use the index associated with the particular network and/or the particular network node in the mapping that applies to a terminal device to identify a particular network and/or a particular network node in communications between the network node and the terminal device in which the particular network and/or the particular network node is to be identified.

According to a ninth aspect, there is provided a computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform any of the method embodiments described above.

According to a tenth aspect, there is provided a terminal device for use in a first network, wherein the terminal device comprises a processor and a memory, said memory containing instructions executable by said processor whereby said terminal device is operative to maintain one or more indices and a mapping between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein two or more networks and/or network nodes share the same index; and determine which one of the two or more networks and/or network nodes having the shared index the terminal device is to take an action in respect of in the event that the terminal device is to take an action in respect of a network and/or network node having an index shared with another network and/or network node.

According to an eleventh aspect, there is provided a terminal device for use in a first network, the terminal device comprising a first module for maintaining one or more indices and a mapping between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein two or more networks and/or network nodes share the same index; and a second module for determining which one of the two or more networks and/or network nodes having the shared index the terminal device is to take an action in respect of in the event that the terminal device is to take an action in respect of a network and/or network node having an index shared with another network and/or network node.

According to a twelfth aspect, there is provided a node for use in a first network, the node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said node is operative to maintain one or more indices and a mapping between the one or more indices and respective network identifiers in an array or a table, each network identifier identifying a network and/or a network node; and use the index associated with the particular network and/or the particular network node to identify the particular network and/or the particular network node in communications between the node and another node in the first network in which a particular network and/or a particular network node is to be identified.

According to a thirteenth aspect, there is provided a node for use in a first network, the node comprising a first module for maintaining one or more indices and a mapping between the one or more indices and respective network identifiers in an array or a table, each network identifier identifying a network and/or a network node; and a second module for using the index associated with the particular network and/or the particular network node to identify the particular network and/or the particular network node in communications between the node and another node in the first network in which a particular network and/or a particular network node is to be identified.

According to a fourteenth aspect, there is provided a network node for use in a first network, the network node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said network node is operative to determine one or more indices and a mapping between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein different mappings are determined for different terminal devices and/or network subscribers; and send the one or more indices and the mapping to another network node in the first network or to a terminal device in the first network.

According to a fifteenth aspect, there is provided a network node for use in a first network, the network node comprising a first module for determining one or more indices and a mapping between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein different mappings are determined for different terminal devices and/or network subscribers; and a second module for sending the one or more indices and the mapping to another network node in the first network or to a terminal device in the first network.

According to a sixteenth aspect, there is provided a network node for use in a first network, the network node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said network node is operative to maintain one or more indices and one or more mappings between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein different mappings apply to different terminal devices and/or network subscribers; and use the index associated with the particular network and/or the particular network node in the mapping that applies to a terminal device to identify a particular network and/or a particular network node in communications between the network node and the terminal device in which the particular network and/or the particular network node is to be identified.

According to a seventeenth aspect, there is provided a network node for use in a first network, the network node comprising a first module for maintaining one or more indices and one or more mappings between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein different mappings apply to different terminal devices and/or network subscribers; and a second module for using the index associated with the particular network and/or the particular network node in the mapping that applies to a terminal device to identify a particular network and/or a particular network node in communications between the network node and the terminal device in which the particular network and/or the particular network node is to be identified.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the techniques introduced in this document are described below with reference to the following figures, in which:

FIG. 1 is a non-limiting example block diagram of an LTE cellular communications network;

FIG. 2 is a block diagram of a terminal device according to an embodiment;

FIG. 3 is a block diagram of a radio access network node according to an embodiment;

FIG. 4 is a block diagram of a core network node according to an embodiment;

FIG. 5 is a block diagram of a WLAN access point according to an embodiment;

FIG. 6 illustrates an exemplary method of operating a terminal device;

FIG. 7 illustrates an exemplary method of operating a network node;

FIG. 8 illustrates another exemplary method of operating a network node;

FIG. 9 is a diagram illustrating one example of a network interworking feature;

FIG. 10 is a flow chart illustrating a method of operating a terminal device according to an embodiment;

FIG. 11 is a flow chart illustrating a method of operating a network node according to another embodiment;

FIG. 12 is a flow chart illustrating a method of operating a network node according to an embodiment;

FIG. 13 is a flow chart illustrating a method of operating a node according to another embodiment; and

FIG. 14 is a flow chart illustrating a specific embodiment of the techniques described herein.

DETAILED DESCRIPTION

The following sets forth specific details, such as particular embodiments for purposes of explanation and not limitation. But it will be appreciated by one skilled in the art that other embodiments may be employed apart from these specific details. In some instances, detailed descriptions of well known methods, nodes, interfaces, circuits, and devices are omitted so as not obscure the description with unnecessary detail. Those skilled in the art will appreciate that the functions described may be implemented in one or more nodes using hardware circuitry (e.g., analog and/or discrete logic gates interconnected to perform a specialized function, ASICs, PLAs, etc.) and/or using software programs and data in conjunction with one or more digital microprocessors or general purpose computers. Nodes that communicate using the air interface also have suitable radio communications circuitry. Moreover, the technology can additionally be considered to be embodied entirely within any form of computer-readable memory, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor and also in some cases a receiver component and/or transmitter component to carry out the techniques described herein.

Hardware implementation may include or encompass, without limitation, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions.

In terms of computer implementation, a computer is generally understood to comprise one or more processors, one or more processing units, one or more processing modules or one or more controllers, and the terms computer, processor, processing unit, processing module and controller may be employed interchangeably. When provided by a computer, processor, processing unit, processing module or controller, the functions may be provided by a single dedicated computer, processor, processing unit, processing module or controller, by a single shared computer, processor, processing unit, processing module or controller, or by a plurality of individual computers, processors, processing units, processing modules or controllers, some of which may be shared or distributed. Moreover, the terms “processor”, “processing unit”, “processing module” or “controller” also refer to other hardware capable of performing such functions and/or executing software, such as the example hardware recited above.

Although the description is given for a terminal device or user equipment (UE), it should be understood by the skilled in the art that “terminal device” and “UE” are non-limiting terms comprising any mobile, non-mobile or wireless device or node equipped with a radio interface allowing for at least one of: transmitting signals in uplink (UL) and receiving and/or measuring signals in downlink (DL). A UE herein may comprise a UE (in its general sense) capable of operating or at least performing measurements in one or more frequencies, carrier frequencies, component carriers or frequency bands. It may be a “UE” operating in single- or multi-radio access technology (RAT) or multi-standard mode. As well as “UE” and “terminal device”, the term “mobile device” is used interchangeably in the following description, and it will be appreciated that such a device does not necessarily have to be mobile in the sense that it is carried by a user. Instead, the term “mobile device”, as with “terminal device” encompasses any device that is capable of communicating with communication networks that operate according to one or more mobile communication standards, such as GSM, UMTS, LTE, etc.

A cell is associated with a radio access network (RAN) node, where a RAN node comprises in a general sense any node transmitting radio signals in the downlink (DL) to a terminal device and/or receiving radio signals in the uplink (UL) from a terminal device. Some example RAN nodes, or terms used for describing RAN nodes, are base station, eNodeB, eNB, NodeB, macro/micro/pico/femto radio base station, home eNodeB (also known as femto base station), relay, repeater, sensor, transmitting-only radio nodes or receiving-only radio nodes. A RAN node may operate or at least perform measurements in one or more frequencies, carrier frequencies or frequency bands and may be capable of carrier aggregation. It may also be a single-radio access technology (RAT), multi-RAT, or multi-standard node, e.g., using the same or different base band circuitry for different RATs.

It should be noted that unless otherwise indicated, the use of the general term “network node” as used herein refers to a RAN node, such as a base station, an eNodeB, a network node in the RAN responsible for resource management, such as a radio network controller (RNC), a core network node, such as a mobility management entity (MME) or serving gateway (SGW), or a WLAN Access Point (AP).

The signalling described is either via direct links or logical links (e.g. via higher layer protocols and/or via one or more network nodes). For example, signalling from a coordinating node may pass another network node, e.g., a radio node.

FIG. 1 shows an example diagram of an evolved UMTS Terrestrial Radio Access Network (EUTRAN) architecture as part of an LTE-based communications system 2. Nodes in the core network 4 include one or more Mobility Management Entities (MMEs) 6, a key control node for the LTE access network, and one or more Serving Gateways (SGWs) 8 which route and forward user data packets while acting as a mobility anchor. They communicate with base stations 10 in the RAN referred to in LTE as eNBs or eNodeBs, over an interface, for example an S1 interface. The eNBs 10 can include the same or different categories of eNBs, e.g. macro eNBs, and/or micro/pico/femto eNBs. The eNBs 10 communicate with each other over an interface, for example an X2 interface. The S1 interface and X2 interface are defined in the LTE standard. A UE 12 can receive downlink data from and send uplink data to one of the base stations 10 with that base station 10 being referred to as the serving base station of the UE 12. An access point (AP) 14 that is part of a WLAN is also shown in FIG. 1, although it will be appreciated that the WLAN and AP 14 are not part of the EUTRAN architecture.

FIG. 2 shows a terminal device 12 or user equipment (UE) that can be adapted for use in one or more of the non-limiting example embodiments described. The terminal device 12 comprises a processing unit 30 that controls the operation of the terminal device 12. The processing unit 30 is connected to a receiver or a transceiver 32 (which comprises a receiver and a transmitter) with associated antenna(s) 34 which are used to receive signals from or both transmit signals to and receive signals from one or more different types of radio access network (e.g. two or more radio access networks that are operating according to different radio access technologies, RATs), such as RAN node 10 in the LTE network 2 and access point (AP) 14 in a WLAN. The terminal device 12 also comprises a memory unit 36 that is connected to the processing unit 30 and that stores computer program code and other information and data required for the operation of the terminal device 12.

FIG. 3 shows a RAN node 10 (for example a base station, NodeB or an eNodeB) that can be adapted for use in example embodiments described. The RAN node 10 comprises a processing unit 40 that controls the operation of the base station 10. The processing unit 40 is connected to a transmitter or a transceiver 42 (which comprises a receiver and a transmitter) with associated antenna(s) 44 which are used to transmit signals to, and receive signals from, terminal devices 12 in the network 2. The RAN node 10 also comprises a memory unit 46 that is connected to the processing unit 40 and that stores computer program code and other information and data required for the operation of the RAN node 10. The RAN node 10 also includes components and/or circuitry 48 for allowing the RAN node 10 to exchange information with other RAN nodes 10 (for example via an X2 interface) and components and/or circuitry 49 for allowing the RAN node 10 to exchange information with nodes in the core network 4 (for example via the S1 interface). It will be appreciated that RAN nodes for use in other types of network (e.g. UTRAN or WCDMA RAN) may include similar components to those shown in FIG. 3 and may, if appropriate, include interface circuitry 48, 49 for enabling communications with the other network nodes in those types of networks (e.g. other base stations, mobility management nodes and/or nodes in the core network).

FIG. 4 shows a core network node 6, 8 that can be adapted for use in the example embodiments described. The node 6, 8 comprises a processing unit 50 that controls the operation of the node 6, 8. The processing unit 50 is connected to components and/or circuitry 52 for allowing the node 6, 8 to exchange information with RAN nodes 10 with which it is associated (which is typically via the S1 interface). The node 6, 8 also comprises a memory unit 56 that is connected to the processing unit 50 and that stores computer program code and other information and data required for the operation of the node 6, 8.

FIG. 5 shows a WLAN AP 14 that can be adapted for use in the example embodiments described. The AP 14 comprises a processing unit 60 that controls the operation of the AP 14. The processing unit 60 is connected to a transmitter or a transceiver 62 (which comprises a receiver and a transmitter) with associated antenna(s) 64 which are used to transmit signals to, and receive signals from, terminal devices 12. The AP 14 also comprises a memory unit 66 that is connected to the processing unit 60 and that stores computer program code and other information and data required for the operation of the AP 14. The AP 14 also includes components and/or circuitry 68 for connecting the AP 14 to a telephone line or other broadband connection.

It will be appreciated that only the components of the terminal device 12, RAN node 10, core network node 6, 8 and AP 14 that are useful to explain the embodiments presented herein are illustrated in FIGS. 2, 3, 4 and 5.

As noted above, it is often useful or required to communicate network identifiers, which identify a particular network or a particular network node (such as an eNB or WLAN AP), between a terminal device and a network node, or between network nodes. These network identifiers can include identifiers used in WLANs (i.e. WLAN identifiers), such as a Service Set Indicator (SSID), a basic SSID, BSSID, an extended SSID, ESSID, a homogenous ESSID, HESSID, a Realm identifier, a Network Access Indicator, NAI, a public land mobile network, PLMN, identifier, or a Domain Name list, as well as identifiers for networks operating according to other radio access technologies (RATs). It will be appreciated that some network identifiers identify both a network and a particular network node. For example a HESSID identifies both a network and a particular WLAN. A HESSID is the BSSID of a certain WLAN AP in a group of APs, and the BSSID of this selected WLAN AP is also used to identify the group of APs.

Since these network identifiers can be quite large, for example, a Service Set Indicator (SSID) may be up to 32 bytes, and it may often be necessary to communicate a number of network identifiers, it is desirable for there to be a technique for the efficient communication of network identifiers between a terminal device and a network node or between network nodes, in order to minimise the signalling required and avoid unnecessarily decreasing system capacity, increasing terminal device power consumption and generating interference.

Thus according to the techniques described herein, to reduce the amount of signaling between the network node and the terminal device (and between network nodes) an identifier-to-index mapping is introduced so that the indices can be signaled instead of explicitly signaling the network identifiers.

In this technique, a mapping between network identifiers and indices is determined. This mapping can be determined by a network node in the radio access network (RAN) or core network (CN), such as an eNB/RNC/MME/etc. The network node can then signal this mapping to a terminal device and/or other network nodes (e.g. from a CN node to one or more RAN nodes, or from a RAN node to other RAN nodes). The indices provided by the mapping can then be used in communications between the network and the terminal device or between network nodes, which avoid having to use the network identifiers themselves in the communications. The indices act as a ‘common language’ between the network and the terminal or between the network nodes.

FIG. 6 illustrates an exemplary method of operating a terminal device. Thus, in a first step, step 101, the terminal device 12 maintains one or more indices and a mapping between the one or more indices and respective network identifiers. Each of the network identifiers identifies a network and/or a network node. The indices and mapping can be maintained by storing them in the memory unit 36 of the terminal device 12 or reading them from broadcast or dedicated signalling from the network.

The network identifiers preferably relate to network(s) and/or network nodes in a network other than the first network 2 (although in some embodiments they can relate to network nodes in the same network). The network and/or network nodes can be operating according to the same or a different RAT to the first network 2.

The indices and mapping maintained in step 101 may have been received from the first network 2. In other implementations, the terminal device 12 may receive a list and/or sequence of network identifiers from the first network 2 and determine the one or more indices and the mapping based on the position of each network identifier in the received list and/or sequence.

Various different implementations relating to the form of the indices and mapping are described in more detail below.

After maintaining (e.g. storing or reading) the one or more indices and the mapping, in communications between the terminal device 12 and a first network 2 in which a particular network and/or a particular network node (e.g. WLAN AP 14) is to be identified, the terminal device 12 uses the index associated with the particular network and/or the particular network node to identify the particular network and/or the particular network node (step 103). As described in more detail below, these communications can comprise downlink communications from the first network 2 that include an index or indices relating to one or more networks and/or network nodes to be identified to the terminal device 12, uplink communications from the terminal device 12 to the first network 2 that include an index or indices relating to one or more networks and/or network nodes to be identified to the first network 2, or both uplink and downlink communications.

FIG. 7 illustrates an exemplary method of operating a network node 10 of a first network 2. The network node may be a node in the RAN of the first network (in which case the network node can be an eNB, RNC or WLAN AP). In a first step, step 111, the network node 10 maintains one or more indices and a mapping between the one or more indices and respective network identifiers. Each of the network identifiers identifies a network and/or a network node (e.g. an eNB or WLAN AP). The indices and mapping can be maintained by storing them in the memory unit 46 of the network node 10.

The network identifiers preferably relate to network(s) and/or network nodes in a network other than the first network 2 (although in some implementations they can relate to network nodes in the same network). The network and/or network nodes can be operating according to the same or a different RAT to the first network 2.

The indices and mapping maintained in step 111 may have been received from a network node 6 in the core network 4 the first network 2 or another network node 10 in the RAN. In other implementations, the network node 10 may determine the one or more indices and mapping from a list and/or sequence of network identifiers.

Various different implementations relating to the form of the indices and mapping are described in more detail below.

After maintaining the one or more indices and mapping, in communications between the network node 10 and a terminal device 12 or another network node 10 in which a particular network and/or a particular network node is to be identified, the network node 10 uses the index associated with the particular network and/or the particular network node to identify the particular network and/or the particular network node (step 113). As described in more detail below, these communications can comprise downlink communications from the network node 10 to the terminal device 12 that include an index or indices relating to one or more networks and/or network nodes to be identified to the terminal device 12, uplink communications from the terminal device 12 to the network node 10 that include an index or indices relating to one or more networks and/or network nodes to be identified to the first network 2 by the terminal device 12, or both uplink and downlink communications.

In some implementations, a network node may be responsible for determining the one or more indices and mapping and providing these to other network nodes. A method of operating a network node according to this implementations is shown in FIG. 8. This method may be performed in a RAN node 10, such as an eNB, RNC or WLAN AP, or a node 6 in the core network 4, such as an MME.

Thus, in step 121, the network node 6 determines one or more indices and a mapping between the one or more indices and respective network identifiers. Each of the network identifiers identifies a network and/or a network node (e.g. an eNB or WLAN AP).

The network identifiers may relate to network(s) and/or network nodes in a network other than the network in which the network node 6 is operating, but in other embodiments they can relate to network nodes in the same network.

The network node 6 then sends the one or more indices and the mapping to a network node 10, for example in the RAN of the network, and/or to a terminal device 12 in the network (step 123).

In the following explanation of the techniques provided herein, the specific example of WLAN identifiers is used, but it will be appreciated that the techniques described below are equally applicable to other types of network identifiers.

In the following various implementations are described of how a network node associates an index to a network (e.g. WLAN) identifier (which herein will be referred to as identifier-to-index mapping) are described, how a network node communicates these indices and the mapping to the terminal device or to another network node, and how the index can be used in communications between the network node and the terminal devices to reduce signaling overhead.

As noted above the network node sending this mapping may be an eNB, NB, RNC or similar. As noted above in FIG. 8, in some implementations one network node assigns the indices to the identifiers and this assignment is then used by other network nodes. For example, it will be described below how an MME establishes the identifier to index mapping, and the mapping is used by another network node such as an eNB in its communication with a terminal device.

Although the identifier-to-index mapping is not limited to use in specific situations, protocols or mechanisms, the following description of the identifier-to-index mapping relates to its use in a 3GPP/WLAN interworking mechanism. The interworking mechanism may relate to any one or more of access network selection, traffic steering (where all of a user's traffic or a certain part of a user's traffic is steered to a particular network) and aggregation (where a user's traffic may be split between carriers with networks operating according to different RATs, e.g. a carrier to a WLAN and a carrier to a 3GPP network). Thus, one exemplary use of the techniques is where a 3GPP network node (i.e. a network node in a 3GPP network), such as an eNB, signals WLAN identifiers to a terminal device. The eNB may associate an index or indices with the WLAN identifiers and signal this mapping to the terminal device. This mapping can then be used in communication between the network and the terminal device by referring to the indices instead of the WLAN identifiers.

Two exemplary interworking mechanisms in which the techniques can be applied, the threshold-based mechanism and traffic steering command based mechanism mentioned above, are described in more detail below. These mechanisms/solutions are described in 3GPP TR 37.834 v12.0.0 (2013-December) “Study on Wireless Local Area Network (WLAN)—3GPP radio interworking (Release 12)” as Solutions 2 and 3 respectively.

Solution 2

As noted above, in the threshold based mechanism the 3GPP network (i.e. network node of the first RAT) provides to the UE conditions and/or thresholds which are used by the UE in one or more pre-defined rules dictating when the terminal device should steer traffic from one RAT to the other.

For example, a pre-defined rule could be of the form shown in Table 1 where threshold1, threshold2, threshold3 and threshold4 are provided to the UE by the 3GPP network, i.e. a network node of the first RAT such as an eNodeB, Node B or RNC.

TABLE 1 Example of the threshold based mechanism if (3GPP signal < threshold1) && (WLAN signal > threshold2) {   steerTrafficToWLAN( ); } else if (3GPP signal > threshold3) || (WLAN signal < threshold4) {   steerTrafficTo3gpp( ); }

This exemplary rule provides that if the UE measured 3GPP signal is below threshold1 and the UE measured WLAN signal is above threshold2 then the terminal device steers traffic to WLAN. Otherwise, if the 3GPP signal is above threshold3 and the WLAN signal is below threshold4 the terminal device steers traffic to 3GPP.

The term ‘3GPP signal’ herein could mean the signal transmitted by a radio network node belonging to a 3GPP RAT, e.g. a node in a LTE, HSPA, GSM etc. network, and/or it could be the quality of such a signal. The term ‘WLAN signal’ herein could mean the signal transmitted by a radio network node belonging to WLAN, e.g. an access point (AP) etc., and/or it could be the quality of such a signal. Examples of measurements of 3GPP signals include are reference signal received power (RSRP) and reference signal received quality (RSRQ) in LTE or common pilot channel (CPICH) received signal code power (RSCP) and CPICH Ec/No in HSPA. Examples of measurements of WLAN signals are Received Signal Strength Indicator (RSSI), Received Channel Power Indicator (RCPI), Received Signal to Noise Indicator (RSNI), etc.

A high level description of this threshold based mechanism is provided below and also in 3GPP TS 36.300 v12.2.0

23.6 Access network selection and traffic steering between E-UTRAN and WLAN

This section describes the mechanisms to support traffic steering between E-UTRAN and WLAN.

23.6.1 General Principles

This version of the specification supports E-UTRAN assisted UE based bi-directional traffic steering between E-UTRAN and WLAN for UEs in RRC_IDLE and RRC_CONNECTED.

E-UTRAN provides assistance parameters via broadcast and dedicated RRC signalling to the UE. The RAN assistance parameters may include E-UTRAN signal strength and quality thresholds, WLAN channel utilization thresholds, WLAN backhaul data rate thresholds, WLAN signal strength and quality thresholds and Offload Preference Indicator (OPI). E-UTRAN can also provide a list of WLAN identifiers to the UE via broadcast signalling. WLANs provided by E-UTRAN may include an associated priority.

The UE uses the RAN assistance parameters in the evaluation of:

-   -   Traffic steering rules defined in TS 36.304 [11]; or     -   ANDSF policies defined in TS 24.312 [58]         for traffic steering decisions between E-UTRAN and WLAN as         specified in TS 23.402[19].

The OPI is only used in ANDSF policies as specified in TS 24.312 [58].

WLAN identifiers are only used in traffic steering rules defined in TS 36.304 [11].

If the UE is provisioned with ANDSF policies it shall forward the received RAN assistance parameters to upper layers, otherwise it shall use them in the traffic steering rules defined in section 23.6.2 and TS 36.304 [11]. The traffic steering rules defined in section 23.6.2 and TS 36.304 [11] are applied only to the WLANs of which identifiers are provided by the E-UTRAN.

The UE in RRC_CONNECTED shall apply the parameters obtained via dedicated signalling if such have been received from the serving cell; otherwise, the UE shall apply the parameters obtained via broadcast signalling.

The UE in RRC_IDLE shall keep and apply the parameters obtained via dedicated signalling, until cell reselection or a timer has expired since the UE entered RRC_IDLE upon which the UE shall apply the parameters obtained via broadcast signalling. In the case of RAN sharing, each PLMN sharing the RAN can provide independent sets of RAN assistance parameters.

23.6.2 Access Network Selection and Traffic Steering Rules

The UE indicates to upper layers when (and for which WLAN identifiers along with associated priorities, if any) access network selection and traffic steering rules defined in TS 36.304 [11] are fulfilled. The selection among WLAN APs that fulfil the access network selection and traffic steering rules is up to UE implementation.

When the UE applies the access network selection and traffic steering rules defined in TS 36.304 [11], it performs traffic steering between E-UTRAN WLAN with APN granularity.

User preference takes precedence (FFS whether it does not apply to particular scenarios).

Solution 3

As noted above, in the traffic steering command based mechanism, the (3GPP) network configures the terminal device to send measurement reports related to WLANs the terminal device has discovered (or to WLANs for which certain conditions have been fulfilled). The network would, based on these measurement reports, decide whether the terminal device shall steer traffic towards the reported WLANs. If a terminal device is to steer traffic towards a WLAN, the network sends a traffic steering command to that terminal device.

The following detailed description of this solution is also found in section 6.1.3 of TR 37.834:

In this solution the traffic steering for UEs in RRC CONNECTED/CELL_DCH state is controlled by the network using dedicated traffic steering commands, potentially based also on WLAN measurements (reported by the UE).

For UEs in IDLE mode and CELL_FACH, CELL_PCH and URA_PCH states the solution is similar to solution 1 or 2 [as described in TR 37.834].

Alternatively, UEs in those RRC [Radio Resource Control] states can be configured to connect to RAN and wait for dedicated traffic steering commands.

Overall description—As an example, traffic steering for UEs in RRC CONNECTED/CELL_DCH comprises the following steps as shown in FIG. 9.

Step 201. Measurement control: The eNB/RNC configures the UE measurement procedures including the identity of the target WLAN to be measured.

Step 202. Measurement report: The UE is triggered to send MEASUREMENT REPORT by the rules set by the measurement control.

Step 203. Traffic steering: The eNB/RNC sends the steering command message to the UE to perform the traffic steering based on the reported measurements and loading in the RAN.

The above procedures do not take into account user preference and/or the WLAN radio state. For example, based on user preferences and/or WLAN radio state, a UE may not be able to perform the configured measurement events. Additionally, the procedures need to allow a UE to be able to prioritize non-operator WLAN over operator WLAN. For example, the UE may disassociate from the operator WLAN and associate with the higher priority non-operator WLAN at any time during the measurement process.

The procedure illustrated above, and the following description can apply to UMTS CELL_FACH as well. The procedure can also be extended to UMTS/LTE Idle modes and UMTS CELL/URA_PCH states, e.g. UEs may be configured to report some indication (e.g. on available WLAN measurements) in a RRC UL message, e.g., RRC connection request (from Idle, in UMTS/LTE) or CELL UPDATE (in UMTS CELL/URA_PCH states).

Some of the steps above, e.g. steps 201 & 202, can be optional, based on RAN/UE configuration.

Step 201: Measurement control—For measurement control, the following examples are types of information can be configured for the UE to measure the operator WLAN:

1. Measurement events to trigger reporting as defined in Table 2 below

2. Target identification as defined in Table 3 below

3. Measurements to report as defined in Table 4 below

Based on the measurement events defined in 3GPP TS 36.331 [“Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification”] and 3GPP TS 25.331 [“Radio Resource Control (RRC); Protocol Specification”], Table 2 shows the candidate measurement events for WLAN:

TABLE 2 Candidate measurement events for reporting WLAN Event Description W1 WLAN becomes better than a threshold (to trigger traffic steering to WLAN) W2 WLAN becomes worse than a threshold (to trigger traffic steering from WLAN) W3 3GPP Cell's radio quality becomes worse than threshold1 and WLAN's radio quality becomes better than threshold2 (to trigger traffic steering to WLAN) W4 WLAN's radio quality becomes worse than threshold1 and 3GPP Cell's radio quality becomes better than threshold2 (to trigger traffic steering from WLAN)

The thresholds are based on the values of the measurements to report defined in Table 4 below.

The target identification is used to indicate to the UE which WLAN to consider for the measurement control procedures including the target WLAN ID and the operating channels to search for. Table 3 shows the candidate target identifiers for WLAN.

For steering traffic from WLAN, i.e., W2/W4, it may be sufficient that just the serving WLAN below a threshold is reported, i.e. the WLAN target identifiers are not needed.

TABLE 3 Candidate target identifiers for WLAN Availability Identifier Description in WLAN BSSID Basic Service Set Identifier: For Beacon or infrastructure BSS, the BSSID is the MAC Probe address of the wireless access point Response SSID Service Set Identifier: The SSID can be Beacon or used in multiple, possibly overlapping, Probe BSSs Response HESSID Homogeneous Extended Service Set Beacon or Identifier: A MAC address whose value Probe shall be configured by the Hotspot Operator Response with the same value as the BSSID of one of (802.11) the APs in the network. All APs in the wireless network shall be configured with the same HESSID value. Domain Domain Name List element provides a list ANQP Name List of one or more domain names of the entity (HS 2.0) operating the WLAN access network. Operating Indication of the target WLAN frequency. N/A class, See Annex E of 802.11 [5] for channel definitions of the different number operating classes NOTE: If above information is not available in eNB/RNC, it is possible for RAN to configure general WLAN measurements

Step 202: Measurement report—Table 4 shows the candidate measurements to report for WLAN.

TABLE 4 Candidate measurement to report for WLAN Availability Identifier Description in WLAN RCPI Received Channel Power Indicator: Measure of the received RF Measurement power in the selected channel for a received frame in the range of −110 to 0 dBm RSNI Received Signal to Noise Indicator: An indication of the signal to Measurement noise plus interference ratio of a received IEEE 802.11 frame. Defined by the ratio of the received signal power (RCPI-ANPI) to the noise plus interference power (ANPI) in steps of 0.5 dB in the range from −10 dB to +117 dB BSS Contains information on the current STA population and traffic levels Beacon or Load in the BSS. Probe Response (802.11k) WAN Includes estimates of DL and UL speeds and loading as well as link ANQP (HS metrics status and whether the WLAN AP is at capacity. 2.0)

Step 203: Traffic steering—In order for RAN to control traffic routing (if agreed to be supported) if ANDSF [Access Network Discovery and Selection Function] is not used, the RAN would need to know which APNs [Access Point Names]/bearers may be (not) offloaded. The RAN also needs means to inform the UEs accordingly so that e.g. the UE can issue the corresponding binding update with the CN over S2c. This would impact signalling between CN and eNB as well as the UE behaviour between AS and NAS level. Table 5 shows candidate examples for identifying the traffic to steer to or from WLAN.

TABLE 5 Candidate identifiers of the traffic to steer to or from WLAN Identifier Description DRB/RB-ID Identity of a radio bearer QCI QoS Class Identifier

Establishing the mapping between network identifiers and indices

In some implementations the indices are numerical values. The index may therefore be an integer value. Possible ranges are 0-15, 1-16, etc, although the range can depend on how many network identifiers there are. The mapping would then indicate the associated numerical value for each WLAN identifier. One example how this mapping could be communicated from a network node 10 to a terminal device 12 in RRC is illustrated below where the information element wlan-identifierindex indicates which index the associated identifier has:

WLAN-IdPerPLMN-r12 ::= SEQUENCE {  wlan-Identifiers CHOICE {   ssid OCTET STRING (SIZE (1..32)),   bssid OCTET STRING (SIZE (6)),   hessid OCTET STRING (SIZE (6))  },  wlan-identifierIndex INTEGER (1..maxWLAN-Id-r12)  OPTIONAL -- Need OR }

In some implementations a default index will be assigned by a terminal device 12 or other network node 10 to a WLAN identifier for which the network has not provided an index. The index may then not need to be signaled to the terminal device 12 or the other network node 10 and additional signaling overhead reduction can be achieved. An example how this can be implemented in RRC is shown below where the value 0 is the default value for WLAN identifiers.

WLAN-IdPerPLMN-r12 ::= SEQUENCE {  wlan-Identifiers CHOICE {   ssid OCTET STRING (SIZE (1..32)),   bssid OCTET STRING (SIZE (6)),   hessid OCTET STRING (SIZE (6))  },  wlan-identifierIndex INTEGER (1..maxWLAN-Id-r12)  DEFAULT    0 }

This index may alternatively be an alphanumeric or alphabetic character. An example of how this can be implemented in RRC is shown below.

WLAN-IdPerPLMN-r12 ::= SEQUENCE {  wlan-Identifiers CHOICE {   ssid OCTET STRING (SIZE (1..32)),   bssid OCTET STRING (SIZE (6)),   hessid OCTET STRING (SIZE (6))  },  wlan-identifierIndex IA5String  OPTIONAL -- Need OR }

In some implementations the mapping is implicit, and it is not necessary for a network node to explicitly signal the mapping and index associated with each identifier since a terminal device 12 or other network node 10 will implicitly know the index of an identifier. One possible way of implementing implicit mapping is for the index to be determined based on the position of the network identifier in a list and/or sequence. For example, a list and/or sequence of WLAN identifiers can be indicated in the following order: SSID A, SSID B, SSID C. The indices could then be mapped as: SSID A has index 1 (or 0), SSID B has index 2 (or 1), SSID C has index 3 (or 2).

In some implementations, the index can be signaled using a priority indicator. The example below shows how a priority indicator can be used. The priority indicator would need to be signaled as a unique value for each network identifier if it is to be possible to distinguish different identifiers (i.e. two WLAN identifiers cannot have the same priority). However, it would be possible for multiple WLAN identifiers to have the same index (i.e. priority indicator in this implementation) in case it is acceptable that the identifiers which share a priority indicator are treated similarly (e.g. the network sends a traffic steering command which targets multiple WLANs).

WLAN-IdPerPLMN-r12 ::= SEQUENCE {  wlan-Identifiers CHOICE {   ssid OCTET STRING (SIZE (1..32)),   bssid OCTET STRING (SIZE (6)),   hessid OCTET STRING (SIZE (6))  },  wlan-Priority INTEGER (1..maxWLAN-Id-r12),  OPTIONAL -- Need OR }

In some implementations the same index may be assigned to multiple network identifiers. This could be done for networks or network nodes that do not need to be treated or considered differently (for example in an access network selection and/or traffic steering mechanism). For example, if in a certain situation WLAN A and WLAN B can be treated similarly those identifiers could be assigned the same index. However if two WLANs should be treated differently, then different indices could be assigned to the two WLANs (for example if one WLAN belongs to the operator and the other WLAN belongs to the operator's partner and may cost more to use, then the operator may want to treat the WLANs differently and hence assign different indices to the two WLANs).

In some implementations multiple indices can be assigned to a network identifier. This allows a WLAN identifier to be assigned one index which is common for multiple WLAN identifiers while also being assigned an index which is unique to that WLAN identifier (or common to a smaller group of identifiers). The benefit of this in an access network selection and/or traffic steering mechanism is that the network 10 and terminal device 12 may use the index that is common for multiple WLAN identifiers (i.e. a low granular index) in situations where it is not important to distinguish those WLAN identifiers, while one unique identifier could also be indicated by using a unique index (i.e. a high granular index). For example, consider a scenario where the traffic steering command based mechanism described above is used and the network wants to perform offloading to WLAN for a terminal device. The network may then request the terminal device 12 perform measurements of multiple WLANs by using the low granular index (so that multiple WLANs are measured). The terminal device 12 would then report back to the network in a measurement report; however in this measurement report it may be important to get measurements per WLAN identifier and hence the terminal device 12 could report the measurements and indicate the high granular index.

Example 1 below shows one possible identifier-to-index mapping. In this example there are two identifiers (BSSID V and BSSID W) which have the same index. This may be used for example if the two WLAN identifiers have some commonality such as belonging to the same SSID. The network may not need to distinguish between BSSID V and BSSID W if these belong to the same SSID. Example 1 also shows how each identifier can have multiple indices (indicated by the additional index in the Index2 column).

Example 1: WLAN identifier to index mapping WLAN identifier Index1 Index2 BSSID U 1 A BSSID V 2 B BSSID W 2 C SSID X 3 D SSID Y 6 E

The mapping may be signaled to a terminal device 12 by a RAN node 10 using broadcast signaling. Signaling the mapping with broadcast signaling will ensure that it does not need to be signaled to each terminal device 12 that needs to receive it, hence radio resources may be saved.

Alternatively, the mapping may be signaled to the terminal device 12 using dedicated signaling. The benefit of using dedicated signaling is that different terminal devices may be provided with different identifier-to-index mappings which could allow for differentiation of terminal devices 12.

In some implementations the mapping can be signaled to a terminal device 12 by a core network node 6 such as an MME. The MME 6 can then inform the terminal device 12 of the mapping using non-access stratum (NAS) signaling. The MME 6 may also signal this mapping to the RAN node 10 (e.g. to an eNB over the S1-interface) so that the RAN node 10 can interpret a communication (e.g. a measurement report) containing indices received from the terminal device 12.

In some implementations the identifier to index mapping can be preconfigured in the terminal device 12. One example is that the indices and mapping is provided to the terminal device 12 on a subscriber identity module (SIM)-card or similar entity. Network nodes (e.g. in the RAN) could then be informed of the appropriate mapping, for example by operations administration and management (OAM) configuration.

When the identifier-to-index mapping has been established and provided to the terminal device 12 and/or RAN node 10 the mapping can be used to reduce the amount of signaling between the terminal device 12 and the network 2 or between network nodes 10 in the network 2. The following section provides some examples of how the identifier-to-index mapping can be used.

Uses of WLAN identifiers

In some implementations the terminal device 12 or network node 10 will, when sending a message to another node (e.g. network node 10 or terminal device 12) in which a WLAN identifier should be conveyed, include the index (or indices) associated with the WLAN identifier instead of e.g. reporting the identifier itself. For example, a terminal device 12 could be configured to report to the network the indices of WLANs for which one or more criteria are fulfilled. Example criteria can include:

-   -   A WLAN has been detected.     -   One or more measured signal metrics of a WLAN node 14 are above         (or below) thresholds.     -   The load and/or capacity of a WLAN node 14 is above (or below) a         threshold.

For example, the terminal device 12 can be configured to report to the 3GPP RAN when it has detected WLAN APs with an SSID X, and the terminal device 12 would then report the index associated with SSID X, e.g. 3 and/or D (as indicated in Example 1 above). In another example, the terminal device 12 may have measured (or received an indication of) that a WLAN with BSSID V has, for example, a load level below 40% and a measured signal strength above 60 dBm, and the terminal device 12 would then report index 2 and/or C (2 and C being the indices for BSSID V in Example 1).

One WLAN AP 14 can have identifiers of different types. For example, a WLAN AP 14 could have an SSID X and a BSSID U. In some implementations, the terminal device 12 will report the index associated with only one identifier associated with a WLAN. For example, if a WLAN node 14 has SSID X with index 3 and has a BSSID U with index 1 the terminal device 12 may be configured to only report either 3 or 1. Which of the multiple indices are to be reported may, for example, be decided based on the type of identifiers. Since BSSIDs are of higher granularity (associated with a specific WLAN node 14) while SSIDs have lower granularity (associated with a group of WLAN APs 14) it would provide more information to the network if the terminal device 12 reports that has detected a certain BSSID instead of detecting a certain SSID, i.e. the UE would in the example above report index ‘1’. It would also be possible for the network to configure the terminal device 12 as to which index the terminal device 12 should apply. In an alternative implementation the terminal device 12 can report all applicable indices for a WLAN. Using the example above, the terminal device 12 would then report both indices ‘3’ and ‘1’.

In implementations where multiple WLANs share an index, it may be the case that multiple WLANs that share an index meet the criteria for sending a measurement report, the terminal device 12 may include in the report information related to one of the multiple WLANs. For example, if the terminal device 12 measures BSSID V and BSSID W and both fulfills a criterion for reporting, then the UE 12 may only include in the report information/measurements relating to one of BSSID V and BSSID W. Which of the multiple WLANs is included may be configured by the network, e.g. by an associated priority. Alternatively, in embodiments of the techniques described herein, the terminal device 12 may decide which of the multiple WLANs (or rather the indices for the multiple WLANs) to include in the report. For example, the terminal device 12 may include the WLAN which has e.g. the strongest signal, the highest signal quality, the lowest air interface load, the highest total capacity or the highest current capacity, etc. It would also be possible for the terminal device to, based on one or more metrics, decide which of the WLANs is “best” by considering several metrics such as signal strength and load.

A method of operating a terminal device according to the above embodiment is shown in FIG. 10. In step 251, one or more indices and a mapping between the one or more indices and respective network identifiers are maintained (e.g. stored) in the terminal device 12 (for example in memory unit 36), with two or more networks or network nodes sharing the same index. In step 253 if the terminal device 12 is to take an action in respect of a network and/or network node having an index shared with another network and/or network node, then the terminal device 12 determines which one of the two or more networks and/or network nodes having the shared index the terminal device is to take the action in respect of. As noted above, this determining can be based on which WLAN has the strongest signal, the highest signal quality, the lowest air interface load, the highest total capacity or the highest current capacity, etc. In the above embodiments, the action comprises the sending of a report (e.g. a measurement report) to the network. In the embodiments below, the action can comprise accessing, steering traffic or aggregating carriers over the network or network node.

In some implementations, the terminal device 12 can indicate to the network how many WLANs matching a certain index fulfill the reporting condition. For example, if the conditions for reporting for BSSID U, BSSID V and BSSID W are fulfilled the terminal device 12 may report index 1 and index 2 (as in Example 1 above). But the terminal device 12 may then according to this embodiment also indicate that there is one node associated with index 1 for which the conditions are fulfilled, and two nodes associated with index 2 for which the conditions are fulfilled.

In some implementations, the network (e.g. 3GPP RAN) may indicate to the terminal device 12 that it is to perform a mobility-related procedure towards a WLAN by signaling the associated index. A mobility-related procedure may be one or many of measurement reporting, traffic steering, access selection, traffic aggregation, etc. Prior to this being done the network would need to indicate the identifier to index mapping, as discussed above. For example, the network may indicate to the terminal device 12 that it is to steer traffic to a WLAN with index 1, and the UE 12 would then (according to the example mapping in Example 1 above) steer traffic to the WLAN with BSSID U. If the network indicates to the terminal device 12 to aggregate traffic over WLAN (and 3GPP) with index 2 then the UE 12 may aggregate traffic over WLAN with BSSID V or BSSID W and over 3GPP.

In some embodiments, if the terminal device 12 is requested to perform an action with respect to a WLAN with a certain index and the terminal device 12 finds multiple candidate WLANs with that index but is only capable of performing the action for one of (or a subset of) the multiple candidates, the terminal device 12 can decide which candidates the action should be performed for (step 253). For example, if the terminal device 12 is requested to steer traffic over a WLAN with index 2 and the terminal device 12 finds both BSSID V and BSSID W (which both have index 2), the UE 12 may select one of the two BSSIDs to apply the action to. As in the above embodiment, which of the multiple WLANs is selected may be determined based on a rule, for example the WLAN with the strongest signal, the highest signal quality, the lowest load, etc. It would also be possible for the terminal device 12 to, based on one or more metrics, decide which of the network nodes is “best” by considering metrics such as signal strength and load. In alternative implementations, the network can configure the terminal device 12 as to which of the multiple candidates the terminal device 12 should perform the action for.

As noted above, it is also possible for the identifier-to-index mapping to be used in other messages/indications/procedures than those described above. For example, another use case for the identifier-to-index mapping is when the network indicates that a terminal device 12 should evaluate an access network selection, traffic steering and/or carrier aggregation mechanism considering only certain WLAN identifiers.

Indication of Whether to use Indices or Network Identifiers

Not all terminal devices, networks, or network nodes, may be capable of using indices instead of network identifiers. Therefore the network could, in some implementations, indicate to the terminal device 12 whether to use indices or to use WLAN identifiers when referring to WLANs. For example, if an LTE eNB is capable of using indices instead of WLAN identifiers, that eNB may indicate to the terminal devices 12 it is serving that signalling of indices should be used, while if another LTE eNB is not capable of using indices instead of WLAN identifiers then that eNB may indicate to the terminal device 12 that signalling of WLAN identifiers should be used.

The indication may be explicitly signalled by the network, for example as a bit-flag indication, which could be signalled using dedicated signalling or broadcast signalling. It may be the case that if this bit-flag has not been signalled to the terminal device 12, the terminal device 12 would interpret this as the network indicating that indices should not be used.

In some implementations it is possible for this indication to be signalled implicitly. The terminal device 12 may consider that the network has indicated that indices should be used if the network signals indices together with the WLAN identifiers, while if the network has not indicated any indices with the WLAN identifiers, the terminal device 12 would consider that the network has indicated that indices should not be used.

Subscription Based Identifier to Index Mapping

In some implementations the identifier-to-index mapping can be signaled to the terminal device 12 by a core network node 4, e.g. an MME. In some embodiments of the techniques described herein this core network node 4 may consider information about the user subscription when determining the identifier-to-index mapping for a terminal device 12. For example, the core network node 4 may provide different index-to-identifier mappings to gold users (e.g. users with expensive or higher value subscriptions) than to bronze users (e.g. users with less expensive or lower value subscriptions). This means that, depending on the subscription, the terminal devices 12 can be handled differently. For example, it will below be explained how a terminal device 12 reports to an RAN node 10 the index associated with a WLAN AP 14 (instead of the identifier for the WLAN AP 14) when the terminal device 12 has detected the WLAN AP 14. If the identifier-to-index mapping has been set differently for terminal devices 12 based on the user subscriptions, then the RAN node 10 can take different approaches with respect to terminal devices 12 with different subscriptions without needing to know the subscription level.

In some embodiments, the RAN may apply different behaviors depending on the index for a WLAN identifier. For example, the RAN may be configured to apply a more aggressive offloading strategy towards WLANs with index 1 compared to WLANs with index 2, i.e. traffic steering towards a WLAN with index 1 may be done at a lower 3GPP load level compared to traffic steering towards a WLAN with index 2. Hence, with the subscription based identifier to index mapping it would be possible that the core network node 4 (e.g. MME) has assigned index 1 for SSID X for a bronze user while assigning index 2 for SSID X for a gold user. This means that the bronze user will report index 1 when it detects a WLAN with SSID X, but a gold user will report index 2, and then the RAN may then offload the bronze user while keeping the gold user in 3GPP (assuming that the 3GPP network is more likely provide a better user experience than WLAN).

Flow charts illustrating the above embodiments are shown in FIGS. 11 and 12. FIG. 11 corresponds to a method of operating a network node (e.g. a core network node or a node in the RAN) that determines the indices and mapping. FIG. 12 corresponds to a method of operating a network node (e.g. a RAN node) that uses the indices and mapping in communications with a terminal device.

Thus, in step 261 of FIG. 11, the network node 6 determines one or more indices and a mapping between the one or more indices and respective network identifiers, with different mappings being determined for different terminal devices and/or network subscribers as described above. In step 263, the mappings and indices are sent to the relevant terminal devices and/or network subscribers for use in communications between the terminal device and the network.

In step 271 of FIG. 12, the network node maintains one or more indices and one or more mappings between the one or more indices and respective network identifiers. Different mappings for different terminal devices and/or network subscribers are maintained. In communications between the network node and a terminal device in which a particular network or a particular network node is to be identified, the network node uses the index associated with the particular network or the particular network node in the mapping that applies to the terminal device or its subscriber to identify the particular network or the particular network node (step 273).

Identifier Handling in Terminal Devices and the Network

In some embodiments the terminal device 12 and/or network may maintain the WLAN identifiers in an array or table, as shown in Example 2 below. The WLAN identifiers would be placed at an entry in the array or table corresponding to the index of the identifier. E.g. if the index of SSID X is 3 then SSID X would be placed in location 3 of the array. It would also be possible for the indices to be offset by an integer, e.g. a WLAN identifier with index X is placed in location X+N where N is a positive or negative integer value.

A method of operating a node in a network according to these embodiments is shown in FIG. 13. The node can be a network node, such as a RAN node 10 or a node 6 in the core network, or a terminal device 12. In step 281, the node maintains one or more indices and a mapping between the one or more indices and respective network identifiers in an array or a table (with each network identifier identifying a network or a network node). Then, in communications between the node and another node in the first network in which a particular network and/or a particular network node is to be identified, the index associated with the particular network and/or the particular network node is used to identify the particular network and/or the particular network node (step 283).

When the terminal device 12 is going to scan for/start reporting for/steer traffic to a WLAN with an index X, the UE would scan for/start reporting for/steer traffic to the corresponding WLANs which are placed at entry X in the array.

Example 2: WLAN identifiers in an array 0 1 BSSID U 2 BSSID V, BSSID W 3 SSID X 4 5 6 SSID Y 7

In case there are multiple identifiers associated with the same index the terminal device 12 may represent this using a two dimensional array where there is a list of identifiers in each array entry.

Specific Embodiment

The flow chart in FIG. 14 illustrates a specific embodiment of the techniques described herein in which an identifier to index mapping is used in a traffic steering command based approach to an access network selection and/or traffic steering. The steps shown in FIG. 14 cover steps performed in both the terminal device and the network (e.g. RAN) node.

Thus, in step 301 a terminal device 12 receives a WLAN identifier to index mapping over broadcast signalling from an eNB 10. The terminal device 12 maintains the mapping in an array (step 303), for example by storing it in a memory unit.

As part of an access network selection and/or traffic steering procedure, the terminal device 12 is requested by the eNB 10 to perform measurement reporting of a WLAN with an index X (step 305).

The terminal device 12 extracts the WLAN identifier(s) associated with index X from the array (step 307) and performs measurements of WLANs having identifier(s) matching the extracted identifier(s) (step 309).

The terminal device 12 constructs a measurement report and indicates the indices for the measured WLANs in the report (step 311). The report is sent to the eNB 10.

The network (eNB 10) receives the measurement report (step 313).

The network extracts from the identifier to index mapping the WLAN identifiers corresponding to the indices in the received report (step 315).

The network then evaluates whether the terminal device 12 should steer traffic to the reported WLANs and if so to which WLAN (step 317). If no traffic steering is to be performed, the method ends (steps 319 and 321). If traffic steering is to be performed, the network indicates to the terminal device 12 that traffic steering should be performed (via a traffic steering command) and includes the index of the WLAN to which traffic should be steered (step 323).

The terminal device 12 receives the indication (traffic steering command) and extracts the WLAN identifier associated with the indicated index from the identifier to index mapping (step 325). The terminal device 12 then performs the traffic steering to the appropriate WLAN (step 327).

Modifications and other variants of the described embodiment(s) will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the embodiment(s) is/are not to be limited to the specific examples disclosed and that modifications and other variants are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Various exemplary embodiments of the techniques described herein are set out below:

1. A method of operating a terminal device in a first network, the method comprising:

-   -   maintaining one or more indices and a mapping between the one or         more indices and respective network identifiers, each network         identifier identifying a network or a network node, wherein two         or more networks or network nodes share the same index; and     -   in the event that the terminal device is to take an action in         respect of a network or network node having an index shared with         another network or network node, the method further comprises         the step of:         -   determining which one of the two or more networks or network             nodes having the shared index the terminal device is to take             the action in respect of.

2. A method as in embodiment 1, wherein the action comprises sending a report to the first network.

3. A method as in embodiment 2, wherein the report is a report indicating one or more measurements of the determined network or network node.

4. A method as in embodiment 3, wherein the action comprises sending a report to the first network in respect of a network or network node for which one or more criteria are fulfilled.

5. A method as in embodiment 4, wherein two or more of the networks or network nodes having a shared index fulfil the criteria, and wherein the step of determining comprises determining which one of the two or more networks or network nodes the report should include the one or more measurements for.

6. A method as in any of embodiments 1-5, wherein the step of determining is performed in the event that the terminal device receives an index from the first network that is shared by two or more networks or network nodes.

7. A method as in embodiment 6, wherein the index is received from the first network with an indication of an action the terminal device is to take with respect to a network or network node associated with the index.

8. A method as in embodiment 7, wherein the action the terminal device is to take is to access, steer traffic and/or aggregate traffic to a network or network node associated with the index.

9. A method as in any of embodiments 1-8, wherein the step of determining comprises determining the network or network node having the shared index to take the action in respect of as the network or network node that has any one or more of:

-   -   (i) the strongest signal;     -   (ii) the highest signal quality;     -   (iii) the lowest air interface load;     -   (iv) the highest total capacity; and     -   (v) the highest current capacity.

10. A method as in any of embodiments 1-9, wherein the action is part of an access network selection, traffic steering and/or traffic aggregation mechanism.

11. A terminal device for use in a first network, the terminal device being adapted to:

-   -   maintain one or more indices and a mapping between the one or         more indices and respective network identifiers, each network         identifier identifying a network or a network node, wherein two         or more networks or network nodes share the same index; and     -   determine which one of the two or more networks or network nodes         having the shared index the terminal device is to take an action         in respect of in the event that the terminal device is to take         an action in respect of a network or network node having an         index shared with another network or network node.

Various other embodiments of the terminal device are contemplated in which the terminal device is further adapted to operate according to any of the above method embodiments.

12. A method of operating a node in a first network, the method comprising:

-   -   maintaining one or more indices and a mapping between the one or         more indices and respective network identifiers in an array or a         table, each network identifier identifying a network or a         network node; and     -   in communications between the node and another node in the first         network in which a particular network or a particular network         node is to be identified, using the index associated with the         particular network or the particular network node to identify         the particular network or the particular network node.

13. A method as in embodiment 12, wherein the step of maintaining comprises placing each network identifier at an entry in the array or table corresponding to the respective index for the network identifier.

14. A method as in embodiment 12, wherein the step of maintaining comprises placing each network identifier at an entry in the array or table that is offset from the respective index for the network identifier.

15. A method as in embodiment 12, 13 or 14, wherein two or more networks or network nodes share the same index and the array is a two-dimensional array.

16. A method as in any of embodiments 12-15, wherein the node is a terminal device.

17. A method as in any of embodiments 12-15, wherein the node is a network node in the first network.

18. A node for use in a first network, the node being adapted to:

-   -   maintain one or more indices and a mapping between the one or         more indices and respective network identifiers in an array or a         table, each network identifier identifying a network or a         network node; and     -   use the index associated with the particular network or the         particular network node to identify the particular network or         the particular network node in communications between the node         and another node in the first network in which a particular         network or a particular network node is to be identified.

Various other embodiments of the node are contemplated in which the node is further adapted to operate according to any of the above method embodiments.

19. A method of operating a network node in a first network, the method comprising:

-   -   determining one or more indices and a mapping between the one or         more indices and respective network identifiers, each network         identifier identifying a network or a network node, wherein         different mappings are determined for different terminal devices         and/or network subscribers; and     -   sending the one or more indices and the mapping to another         network node in the first network or to a terminal device in the         first network.

20. A method as in embodiment 19, wherein the step of determining comprises determining a first mapping for terminal devices and/or network subscribers having a first subscription level and determining a second mapping for terminal devices and/or network subscribers having a second subscription level.

21. A network node for use in a first network, the network node being adapted to

-   -   determine one or more indices and a mapping between the one or         more indices and respective network identifiers, each network         identifier identifying a network or a network node, wherein         different mappings are determined for different terminal devices         and/or network subscribers; and     -   send the one or more indices and the mapping to another network         node in the first network or to a terminal device in the first         network.

Various other embodiments of the network node are contemplated in which the network node is further adapted to operate according to any of the above method embodiments.

21. A method of operating a network node in a first network, the method comprising:

-   -   maintaining one or more indices and one or more mappings between         the one or more indices and respective network identifiers, each         network identifier identifying a network or a network node,         wherein different mappings apply to different terminal devices         and/or network subscribers; and     -   in communications between the network node and a terminal device         in which a particular network or a particular network node is to         be identified, using the index associated with the particular         network or the particular network node in the mapping that         applies to the terminal device to identify the particular         network or the particular network node.

22. A method as in embodiment 21, wherein the communications between the network node and the terminal device comprise communications relating to an access network selection, traffic steering and/or traffic aggregation mechanism.

23. A method as in embodiment 22, further comprising the step of:

-   -   determining an action for the terminal device to take in respect         of the particular network or particular network node, the action         for the terminal device to take being determined based on an         index for the particular network or particular network node         received from the terminal device.

24. A network node for use in a first network, the network node being adapted to:

-   -   maintain one or more indices and one or more mappings between         the one or more indices and respective network identifiers, each         network identifier identifying a network or a network node,         wherein different mappings apply to different terminal devices         and/or network subscribers; and     -   use the index associated with the particular network or the         particular network node in the mapping that applies to a         terminal device to identify a particular network or a particular         network node in communications between the network node and the         terminal device in which the particular network or the         particular network node is to be identified.

Various other embodiments of the network node are contemplated in which the network node is further adapted to operate according to any of the above method embodiments.

In any of the above embodiments each network identifier can identify a network other than the first network or a network node in a network other than the first network. In some embodiments, the network other than the first network is a network that is operating according to a different radio access technology, RAT, to the first network.

In any of the above embodiments the first network is a network operating according to a mobile telecommunications radio access technology, RAT, and the particular network or the particular network node are operating according to a wireless local area network RAT. In some embodiments the mobile telecommunications RAT is a 3GPP-specified RAT. In some embodiments the wireless local area network RAT is WLAN or Wi-Fi.

In any of the above embodiments each network identifier can be an identifier of a WLAN or a network node in a WLAN.

In any of the above embodiments at least one network identifier can be an identifier for an access point, AP, in a WLAN.

In any of the above embodiments at least one network identifier can be a service set identification, SSID, a basic SSID, BSSID, an extended SSID, ESSID, a homogenous ESSID, HESSID, Realm identifier, a Network Access Indicator, NAI, a public land mobile network, PLMN identifier, or a Domain Name list.

In any of the above embodiments each index can comprise a numerical value or an alphanumerical value.

In any of the above embodiments the index can be signalled using a priority value in communications between nodes.

In any of the above embodiments a default value for an index can be used in communications for a network identifier that is not included in the mapping.

In any of the above embodiments two or more networks or network nodes can have the same index. In some embodiments, in the event that at least one of the networks or network nodes having the same index is to be identified in communications, the communications further comprise an indication of how many of said networks or network nodes having the same index the communications apply to.

In any of the above embodiments a network identifier can have two or more associated indices.

In any of the above embodiments, a particular network or a particular network node can have two or more associated network identifiers, each network identifier having a respective index, and in communications in which the particular network or particular network node having the two or more associated network identifiers is to be identified, the one or more of the indices can be used to identify the particular network or the particular network node. In some embodiments the two or more associated network identifiers are different types of network identifiers, and an index for a specific type of network identifier can be used to identify the particular network or the particular network node.

In any of the above embodiments, the indices and mapping are used in communications relating to an access network selection, traffic steering and/or traffic aggregation procedure.

In any of the above embodiments the indices and mapping are used in communications relating to an access network selection, traffic steering and/or traffic aggregation procedure between the first network and a second network operating according to a different radio access technology, RAT, to the first network. In some embodiments each network identifier identifies a particular second network or a particular network node in the second network.

There is also provided a computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform any of the method embodiments described above. 

The invention claimed is:
 1. A method of operating a terminal device in a first network, the method comprising: receiving, from the first network, one or more indices and a mapping between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein a network identifier is mapped to an index which is common for one or more network identifiers while also being mapped to an index which is unique to the network identifier; receiving, from the first network, a communication that specifies a particular index of the one or more indices, wherein the communication includes an instruction to perform a mobility-related action relating to a network and/or network node having the particular index; determining that two or more networks and/or network nodes share the particular index; determining which one of the two or more networks and/or network nodes having the shared index the terminal device is to take the mobility-related action relating to; wherein the mobility-related action comprises sending a report to the first network; and wherein the step of determining comprises determining the network and/or network node having the shared index to take the mobility-related action relating to as the network and/or network node that has any one or more of: (i) the strongest signal; (ii) the highest signal quality; (iii) the lowest air interface load; (iv) the highest total capacity; and (v) the highest current capacity.
 2. The method as in claim 1, wherein the report indicates one or more measurements of the determined network and/or network node.
 3. The method as in claim 2, wherein the mobility-related action comprises sending a report to the first network in respect of a network and/or network node for which one or more criteria are fulfilled.
 4. The method as in claim 3, wherein the two or more of the networks and/or network nodes having the shared index fulfil the criteria, and wherein the step of determining which one of the two or more networks and/or network nodes having the shared index the terminal device is to take the mobility-related action relating to comprises determining which one of the two or more networks and/or network nodes the report should include the one or more measurements for.
 5. The method as in claim 1, wherein the mobility-related action is part of an access network selection, traffic steering and/or traffic aggregation mechanism.
 6. The method of claim 1, wherein the particular index comprises an integer value that maps to an identifier of a wireless local-area network (WLAN).
 7. The method of claim 1, wherein the particular index comprises an integer value that maps to an identifier of a wireless local-area network (WLAN) network node.
 8. The method of claim 1, wherein the respective network identifiers comprise Service Set Identifiers (SSIDs).
 9. The method of claim 1, wherein the mapping comprises an array, wherein the particular index comprises an integer value that indicates a position in the array, and wherein a Service Set Identifier (SSID) of the network and/or network node is stored at the indicated position in the array.
 10. A terminal device for use in a first network, the terminal device being adapted to: receive, from the first network, one or more indices and a mapping between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein a network identifier is mapped to an index which is common for one or more network identifiers while also being mapped to an index which is unique to the network identifier; receive, from the first network, a communication that specifies a particular index of the one or more indices, wherein the communication includes an instruction to perform a mobility-related action relating to a network and/or network node having the particular index; determine that two or more networks and/or network nodes share the particular index; determine which one of the two or more networks and/or network nodes having the shared index the terminal device is to take the mobility-related action relating to; wherein the mobility-related action comprises sending a report to the first network; and wherein the step of determining comprises determining the network and/or network node having the shared index to take the mobility-related action relating to as the network and/or network node that has any one or more of: (i) the strongest signal; (ii) the highest signal quality; (iii) the lowest air interface load; (iv) the highest total capacity; and (v) the highest current capacity.
 11. The terminal device as in claim 10, wherein the two or more of the networks and/or network nodes having the shared index fulfil one or more criteria, and wherein the terminal device is adapted to send a report to the first network and determine which one of the two or more networks and/or network nodes the report should include one or more measurements for.
 12. The terminal device as in claim 10, wherein the mobility-related action is part of an access network selection, traffic steering and/or traffic aggregation mechanism.
 13. A method of operating a node in a first network, the method comprising: maintaining one or more indices and a mapping between the one or more indices and respective network identifiers in an array or a table, each network identifier identifying a network and/or a network node, wherein a network identifier is mapped to an index which is common for one or more network identifiers while also being mapped to an index which is unique to the network identifier; sending, to another node in the first network, a communication that specifies a particular index of the one or more indices, wherein the communication includes an instruction to perform a mobility-related action relating to a network and/or network node having the particular index; wherein the another node determines that two or more networks and/or network nodes share the particular index; wherein the particular index is used to identify which one of the two or more networks and/or network nodes the another node is to take the mobility-related action relating to; wherein the mobility-related action comprises sending a report to the first network; and wherein the step of identifying comprises determining the network and/or network node having the shared index to take the mobility-related action relating to as the network and/or network node that has any one or more of: (i) the strongest signal; (ii) the highest signal quality; (iii) the lowest air interface load; (iv) the highest total capacity; and (v) the highest current capacity.
 14. The method as in claim 13, wherein the step of maintaining comprises placing each network identifier at an entry in the array or table corresponding to the respective index for the network identifier.
 15. The method as in claim 13, wherein the step of maintaining comprises placing each network identifier at an entry in the array or table that is offset from the respective index for the network identifier.
 16. The method as in claim 13, the array is a two-dimensional array.
 17. A method as in claim 13, wherein the node is a network node in the first network.
 18. A node for use in a first network, the node being adapted to: maintain one or more indices and a mapping between the one or more indices and respective network identifiers in an array or a table, each network identifier identifying a network and/or a network node, wherein a network identifier is mapped to an index which is common for one or more network identifiers while also being mapped to an index which is unique to the network identifier; send, to another node in the first network, a communication that specifies a particular index of the one or more indices, wherein the communication includes an instruction to perform a mobility-related action relating to a network and/or network node having the particular index; wherein the another node determines that two or more networks and/or network nodes share the particular index; wherein the particular index is used to identify which one of the two or more networks and/or network nodes the another node is to take the mobility-related action relating to; wherein the mobility-related action comprises sending a report to the first network; and wherein the step of identifying comprises determining the network and/or network node having the shared index to take the mobility-related action relating to as the network and/or network node that has any one or more of: (i) the strongest signal; (ii) the highest signal quality; (iii) the lowest air interface load; (iv) the highest total capacity; and (v) the highest current capacity.
 19. The node as in claim 18, wherein the node is adapted to maintain one or more indices and a mapping between the one or more indices and respective network identifiers by placing each network identifier at an entry in the array or table corresponding to the respective index for the network identifier.
 20. The node as in claim 18, wherein the node is adapted to maintain one or more indices and a mapping between the one or more indices and respective network identifiers by placing each network identifier at an entry in the array or table that is offset from the respective index for the network identifier.
 21. The node as in claim 18, wherein the node is a network node in the first network.
 22. A computer program product comprising a non-transitory computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor residing on a terminal device, the computer or processor is caused to: receive, from a first network, one or more indices and a mapping between the one or more indices and respective network identifiers, each network identifier identifying a network and/or a network node, wherein a network identifier is mapped to an index which is common for one or more network identifiers while also being mapped to an index which is unique to the network identifier; receive, from the first network, a communication that specifies a particular index of the one or more indices, wherein the communication includes an instruction to perform a mobility-related action relating to a network and/or network node having the particular index; determine that two or more networks and/or network nodes share the particular index; and determine which one of the two or more networks and/or network nodes having the shared index the terminal device is to take the mobility-related action relating to; wherein the mobility-related action comprises sending a report to the first network; and wherein the step of determining comprises determining the network and/or network node having the shared index to take the mobility-related action relating to as the network and/or network node that has any one or more of: (i) the strongest signal; (ii) the highest signal quality; (iii) the lowest air interface load; (iv) the highest total capacity; and (v) the highest current capacity. 